The invention relates to a propulsion control system for motor vehicles according to the type shown in DE-PS No. 19 02 944.
The driving stability of a vehicle can be considerably better if it is equipped with a wheel slip control. However, the driving stability is lost when, for example, the cornering limit speed is exceeded. If the gas pedal is not taken back in time, the vehicle becomes unstable.
The arrangement according to DE-PS No. 19 02 944 is a control arrangement for avoiding skidding in turns in the case of motor vehicles. A plurality of measured and calculated quantities are obtained, from gyroscope and several sensors, and provide, in a way that is not shown, control signals for the brake system as well as for a power control element of the internal-combustion engine. In this case, three programs for the varying road conditions are provided that are to be selected by the driver.
This type of system is not satisfactory from the point of view of manufacturing technology because it is much too costly, nor with a view to application. It can be anticipated what happens if the driver forgets to select the program assigned to the actual road conditions. In order to increase the driving stability of vehicles, in addition to the already mentioned wheel slip control, all-wheel drive and antilocking brake systems are also known. However, all these devices cannot keep a vehicle in all cases from exceeding the limits of driving dynamics.
It is the objective of the invention to provide system with simpler means than those that are known which keep a vehicle that has entered the range of the cornering limit speed from entering into the no longer controllable, unstable range.
According to the invention, this objective is achieved by monitoring the lateral acceleration, steering angle and driving speed. The basis is a certain time sequence of the lateral acceleration and of the steering angle and the driving speed. When the vehicle, with increasing driving speed and/or with increasing steering angle, enters into the range of the cornering limit speed, the lateral acceleration suddenly will no longer increase because the tires have already made available the maximum cornering force. The vehicle starts to leave the cornering path. The driver reacts by steering, i.e., by enlarging or reducing the steering angle, according to the lay-out of the vehicle, i.e., according to an oversteering or an understeering of the vehicle.
The invention consists essentially of determining the condition "no change of the lateral acceleration despite change of the steering angle and/of the driving speed" and reacting to it by reducing the power output.
A propulsion system according to the present invention includes circuitry for determining when a predetermined change of steering angle or driving speed is not followed by a change of lateral acceleration. Whereupon the circuitry, which makes a determination activates a storage element to store the momentary value of the steering angle or driving speed. This stored steering angle or driving speed is used to create a first and second threshold to be compared in first and second comparators with the momentary values of the steering angle of driving speed. A bistable circuitry or flip-flop is set by the output signal of the first comparator and reset by the output of the output signal of the second comparator. The output signal of the bistable circuit provides a reduction signal to the reduction of driving torque which is part of a standard propulsion system. the circuitry for determining a predetermined change of steering angle or driving speed includes a differentiator for differentiating the steering angle or driving speed and a comparator for comparing differentiating signal with a predetermined threshold value. A monostable circuit prolongs the output of the comparator since the change of lateral acceleration follows by a specific time delay the monitored driving speed or steering angle. The lack of change of lateral acceleration is determined by a second differentiator with or without a low pass filter at its output and a comparator for comparing the differentiated signal with a predetermined threshold. The comparator provides an output when the differentiating signal falls below the threshold. An AND-gate determines the occurrence of the excessive rate of change of steering angle or driving speed and the lack of change of lateral acceleration to activate the storage device. An additional input to the AND-gate is from a monostable circuit which extends the output signal of the bistable circuit. A time delay circuit connects the output of the bistable circuit with its input to reset the bistable circuit after a predetermined period of time if the output signal is still present.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.